In his new study of Henry Kissinger's role in the last year of the Nixon presidency, Alistair Horne navigates carefully and revealingly in areas that are now the subject of escalating debate between American historians.

The traditional enemies of Nixon hold that he was a uniquely sleazy president who committed crimes in office, and that he chose to squander 30,000 combat soldiers in Vietnam for a spurious "decent interval", rather than extracting the US from that war as soon as he entered office in 1969 by just leaving "by plane and by ship". The same people see Kissinger as completely complicit in Vietnam and somewhat tainted by the alleged ethical turpitude of the administration generally.

On Watergate, Kissinger has finessed the issue of whether Nixon was a felon or not. Nixon himself acknowledged "terrible mistakes unworthy of a president," but never crimes.

Horne seems to find Nixon guilty on the basis of a remark by former CIA director Richard Helms. In the incident referred to, the so-called "smoking gun", Nixon authorised that it be suggested to Helms and his deputy, Vernon Walters, by Nixon's chief of staff, H.R. Haldeman, that the CIA ask the FBI not to look into Watergate because it might lead into undercover CIA Cuban operations. He told Haldeman: "Don't lie to them," and Helms and Walters said they would not act without a direct order from the president. Nixon took it no further. Though tawdry, this is a feeble excuse for chasing a US president from office.

The only plausible argument against Nixon was that he authorised financial assistance to the Watergate defendants in exchange for perjury, disguising White House involvement. This may have happened, but even now it is not entirely clear. In a fair trial, he might well have been acquitted.

Nixon did lie to the country about what he knew of Watergate, but presidential lies are not unconstitutional or infrequent. In this case, when exposed, they vaporised Nixon's political capital. The US national media treated their coverage of both Vietnam and Watergate as triumphs of the crusading press over "imperial" government, and have generally tried to maintain that very convenient conventional wisdom. Re-examination reveals mismanaged official press relations, certainly, but also heavy press biases against the administration.